1. Field of the Invention
The present invention is directed to a head coil for a magnetic resonance apparatus, of the type having a mirror device for the stimulation of one or both eyes with a first light in a first wavelength range and for simultaneous acquisition of a eye movement with a second light in a second wavelength range in a functional magnetic resonance examination.
2. Description of the Prior Art
Functional magnetic resonance imaging enables detection of activity in the human cortex that ensues due to an intentional stimulation. To this end, a repeated stimulus (optical, acoustic, etc.) is usually utilized, and the variation of the oxygen saturation in the blood correlated therewith is detected in images that are T2*-weighted with respect to the intensity of the signals registered with the magnetic resonance apparatus. Optical stimulixe2x80x94due to the structure of clinical magnetic resonance apparatusxe2x80x94are made visible to the patient via an optical mirror device attached in the head coil. In some tasks, the motion of the eyeball should be simultaneously detected in order, for example, to be able to check involuntary movements as well as to be able to check the implementation of certain tasks. Further, eye movements can be utilized as feedback or even control of the stimulus presentation.
For optical stimulation, one or both eyes of the patient are illuminated with light in a first wavelength range, namely visible light. The detection of an eye movement ensues with infrared light that is emitted into one eye. The reflected infrared light is acquired with a reflected light detector and eye movement is detected on the basis of the acquisition result.
In order to be able to simultaneously supply both lights, a mirror device having two mirrors is employed, the one of which reflects the visible light supplied from outside the magnetic resonance apparatus into one or both eyes of the patient and the other reflecting the externally supplied infrared light into at least one eye. The arrangement of the two different mirrors, however, presents significant problems in practical use since the available space in the head coil is very limited. The two mirrors must be arranged such that they do not block one another, otherwise one of the light beams will not be transmitted.
German OS 198 60 037 discloses a magnetic resonance system for topically resolved measurement of the electrical activity of nerve cells. The magnetic resonance system has a magnet for generating a basic magnetic field, coils for generating magnetic gradient fields, and radio-frequency antennas for emitting and receiving radio-frequency pulses. For stimulation of neural activities of a patient to be examined with the magnetic resonance system, a pulse generator generates a stimulation function with which, for example, a light transmitter is driven for optical stimulation of the patient.
Further, German OS 37 20 079 discloses an optical sensor head for measuring the surface of a workpiece that contains an integrated microscope. To this end, a deflection mirror arranged in the wall of the housing of the sensor head is fashioned as a dielectric mirror that is opaque for measurement light and is transparent for at least one light wavelength that is not within the measurement light spectrum.
An object of the present invention is based on the problem of specifying a head coil with a mirror device wherein said difficulties in view of the arrangement are not present.
This object is inventively achieved in a head coil of the type initially described wherein the mirror device has a mirror that reflects the first light and is transmissive for the second light or that is transmissive for the first light and reflects the second light.
In the inventive mirror device, thus, only one mirror is utilized which is a dichroitic mirror, reflecting one light but allowing the other to pass. The possibility of irradiating the mirror with the light for which it is transmissive creates completely new possibilities in view of the light management. Thus, two mirrors are no longer required; on the contrary, one mirror suffices since, due to the possibility of irradiation, the respective light source can be arranged, for example, vertically above the eye region; a beam deflection can be foregone.
It is expedient when the mirror is arranged at an angle between 30xc2x0 and 60xc2x0, particularly an angle of 45xc2x0, relative to the horizontal plane for reflecting a light emitted from the side and for allowing light emitted from the top to pass. One light, for example the visible stimulation light, continues to be emitted from a light source located externally from the magnetic resonance apparatus and is reflected into the eyes of the patient via the mirror, which is preferably arranged at 45xc2x0 relative to the horizontal plane, whereas the second light is emitted in from above.
The mirror thus can be wide enough to extend over both eyes. Alternatively, however, two mirrors arranged next to one another and each allocated to one eye can be provided, these being capablexe2x80x94dependent on the designxe2x80x94of being charged in common or separately with the stimulation light. Expediently, the mirror device is arranged at or in a housing.
In an embodiment of the invention, a device for irradiation of the mirror is provided at the head coil above the mirror or mirrors, this device has a light source for the first light if the mirror is transmissive for this stimulation light or has a light source for the second light and an acquisition device for reflected light. According to this embodiment of the invention, thus, the respective light source, and possibly the acquisition device as well, are provided directly at the head coil. Expediently, the mirror device and the irradiation device are arranged at or in a common housing, so-that a very compact overall structural unit is achieved.
The housing can have an oblique section at which the mirror or mirrors are arranged.
The housing containing the mirror device, potentially the housing containing the irradiation device, or the housing containing both, is detachably arranged at the head coil. This makes it possible to secure the housing or the device to the head coil only when a functional MR examination is to be implemented. For normal examinations, the part is simply removed from the head coil.
In an embodiment of the invention the mirror or mirrors are fashioned as polymer mirrors. Such a mirror is electrically non-conductive, i.e. no eddy currents can arise thereinxe2x80x94different from standard mirrors that are vapor-deposited with metalxe2x80x94in the magnetic fields and radio-frequency fields that are used in the MR examination. Such eddy currents can negatively influence the quality of the magnetic resonance signals. The polymer mirrors can be implemented as film, i.e. the mirror or mirrors are extremely thin; the thickness of a film lies in the range of tenths of a millimeter. Such polymer mirrors can have their reflection and transmission properties set by means of suitable selection of the polymers employed, these being arranged in various layers on top of one another. It is possible without difficulty to design a polymer mirror such that it reflects in the range of visible light between approximately 430 and 700 nm, whereas infrared light having a longer wavelength is allowed to pass.
In addition to the head coil, the invention is also directed to a magnetic resonance apparatus having a head coil of the described type.
The invention also is directed to a separate mirror device for optical stimulation of one or both eyes at the top with a first light in a wavelength range and for simultaneous acquisition of an eye movement with a second light in a second wavelength range, the mirror device being provided for detachable mounting to a head coil of a magnetic resonance apparatus. This mirror device has a housing at or in which at least one mirror is arranged, this mirror reflecting the first light and being transmissive for the second light, or being transmissive for the first light and reflecting the second light.
The mirror should be arranged at an angle between 30xc2x0 and 60xc2x0, particularly at an angle of 45xc2x0, relative to the horizontal plane for reflecting a light emitted from the sidexe2x80x94regardless of whether this is the stimulation light or the infrared light for acquiring movementxe2x80x94and for allowing the light emitted in from above to pass. In addition to one large-area mirror, two mirrors respectively allocated to different eyes can also be provided next to one another.
In an embodiment of the invention, a device for irradiating the mirror is provided in or at the housing above the mirrors or mirror, this device having a light source for the first light or a light source for the second light and an acquisition device for reflection light. A compact structural unit is achieved that contains all relevant componentsxe2x80x94except for an external light source and, if used, the reflection light source and, if used, the reflection light detector, dependent on which light source is integrated at the apparatus sidexe2x80x94and that can be unproblematically secured to the head coil. The transmission properties of the mirror make it possible to provide a light source directed behind the mirror and essentially directly over the eyes of the patient in the mounted position, this light source generating light for which the mirror is transmissive. Normally, this light source would be infrared light source that additionally has an acquisition device for reflection light allocated to it on the basis of which the eye movement is acquired. An extremely compact, small-dimension unit is achieved overall that can be unproblematically secured to the head coil and which occupies extremely little space thereat.
The housing expediently has an oblique section at which the mirror or mirrors are arranged. In order to be able to secure the housing in an optimally simple way, it is expedient when a fastener enabling a plug/latch fastening or a clamp fastening of the housing to the head coil is provided at the housing.
It is also expedient when the irradiation device is displaceably arranged at or in the housing. This is expedient in order to be able to undertake an adjustment of the irradiation device with respect to the eye area of the patient as needed.
It is also expedient when displacement means are provided with which or on which the housing is displaceable relative to the head coil after being fastened to the head coil. This expedient development also serves for adjustability of the mirror device, which is displaceable overall.
The mirror or mirrors are expediently polymer mirrors, which are preferably implemented in film form.